The epoxidation of alkene into alkylene oxide by reacting the alkene with an organic hydroperoxide is known in the art.
For instance, in the method for co-producing propylene oxide and styrene starting from ethylbenzene, the aforementioned epoxidation reaction is applied. In general this co-production process involves the steps of (i) reacting ethylbenzene with oxygen or air to form ethylbenzene hydroperoxide, (ii) reacting the ethylbenzene hydroperoxide thus obtained with propene in the presence of an epoxidation catalyst to yield propylene oxide and 1-phenyl-ethanol, and (iii) converting the 1-phenyl-ethanol into styrene by dehydration using a suitable dehydration catalyst.
Another method for producing alkylene oxide is the coproduction of propylene oxide and methyl tert-butyl ether (MTBE) starting from isobutane and propene. This process involves similar reaction steps as the styrene/propylene oxide production process described in the previous paragraph. In the epoxidation step, tert-butyl hydroperoxide is reacted with propene forming propylene oxide and tert-butanol in the presence of a heterogeneous epoxidation catalyst. Tert-butanol is subsequently etherified with methanol into MTBE, which is used as an additive in motor fuels.
A further method comprises the manufacture of propylene oxide with the help of cumene. In this process, cumene is reacted with oxygen or air to form cumene hydroperoxide. Cumene hydroperoxide thus obtained is reacted with propene in the presence of an epoxidation catalyst to yield propylene oxide and 2-phenyl propanol. The latter may be converted into cumene with the help of a heterogeneous catalyst and hydrogen. Suitable processes are described for example in WO 02/48126.
The present invention concerns the epoxidation reaction between an alkene and an organic hydroperoxide using a heterogeneous catalyst.
Heterogeneous epoxidation catalysts may comprise as the catalytically active metal one or more transition metals, such as vanadium, molybdenum, tungsten, titanium and zirconium. One particularly suitable class of heterogeneous epoxidation catalysts are the titanium-based catalysts. Examples of such catalysts are for instance described in U.S. Pat. No. 4,367,342 and EP-A-0,345,856. U.S. Pat. No. 4,367,342 discloses the use of inorganic oxygen compounds of silicon in chemical composition with at least 0.1% by weight of an oxide or hydroxide of titanium, while EP-A-0,345,856discloses a titania-on-silica heterogeneous catalyst obtainable by impregnating a silicon compound with a stream of gaseous titanium tetrachloride followed by calcination and hydrolysis steps and optionally a silylation step.
When such heterogeneous epoxidation catalysts are used to catalyze the epoxidation of an alkene, the catalyst slowly deactivates. It would be beneficial if the catalyst would keep a high activity for a longer period of time as it would reduce the costs due to catalyst consumption and the time and costs involved in reloading of the reactors. Furthermore, slower deactivation is desirable because in that case the average reaction temperature could be kept lower. It has been found that a lower average reaction temperature generally gives less by-products. Therefore, a higher catalyst activity results in a more cost effective and productive process.
WO 98/32530 describes a process for the production of oxirane compounds by reacting propylene with an organic hydroperoxide using a solid contact catalyst, in which process about 25-75% of the heat of reaction is removed by preheating cold reactor feed by direct contact with a heated propene stream from the reactor. In the process of FIG. 3, the partly converted reaction mixture is divided into two parts, one being recycled and admixed with the cold feed and the other passing to the subsequent catalyst bed. There is no information on the amount of reaction mixture which is recycled or the conversion which has taken place. Furthermore, the reaction mixture which is recycled is substantially free of propylene as propylene is described to be vaporized and removed before the reaction mixture is recycled.
WO 01/12617 teaches that the activity of de-activated catalyst may be restored by contacting the de-activated catalyst with an epoxidation reaction mixture at a temperature which is at least 5° C. higher than the final temperature at which the at least partly deactivated catalyst was in use directly before the start of the re-activation. In Example 1, the de-activated catalyst is contacted with feed while a large recycle stream was maintained over the reactor in order to ensure that the catalyst to be re-activated is contacted with epoxidation reaction product. A throughput of 48 grams/hour of feed with a recycle flow of 2.5 kg/hour makes that more than 98% wt of the product is recycled. WO 01/12617 only uses a large recycle in order to simulate ideal mixing conditions. WO 01/12617 neither teaches nor hints at the use a recycle in the manufacture of alkylene oxide.
WO 01/12617 describes that a typical feed for an epoxidation process comprises 15-25% wt ethylbenzene hydroperoxide, 30-50% wt ethylbenzene, 30-50% wt propene, 0-5% wt 1-phenylethanol and 0-5% wt methylphenylketone, to a total of 100% wt.